Reality check, monkey patch to support newer attrs features.

releasebot.py

@@ -27,6 +27,21 @@ import typing
 import attr
 
 
+# We use type annotations, and attrs implements the helper type keyword
+# for compatibility with python 3.5 in version 17.3.0.
+# We need to monkey patch things.
+if tuple(int(i) for i in attr.__version__.split('.')) < (17, 3, 0):
+    if getattr(attr, 'original_ib', None) is None:
+        attr.original_ib = attr.ib
+        def our_attrib(type=None, *args, **kwargs):
+            # factory is also new in 18.1.0
+            factory = kwargs.pop('factory', None)
+            if factory is not None:
+                kwargs['default']=attr.Factory(factory)
+            return attr.original_ib(*args, **kwargs)
+        attr.ib = our_attrib
+
+
 def _list_helper(
     config, section: str, item: str, separator: str = ","
 ) -> typing.Iterable[str]: